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# Selection Response Principles

GENES-QSQNTU

If a particular distribution of individuals is selected to be parents, relative to all potential parents, the response to selection per generation can be predicted as ${ R }={ i{ h }^{ 2 }\sigma }_{ P }$ where ($i$) is the standardized selection intensity (shown in the table below), ${ h }^{ 2 }$ is heritability (narrow sense heritability), and ${ \sigma }_{ P }$ is the phenotypic standard deviation for the trait under selection pressure.

Assume that in pigs the heritability of weight (in lb) at 240 days of age is 0.40, and the phenotypic variance is 1,156 lb$^2$.

% selected i % selected i % selected i % selected i
0.01 2.67 0.11 1.71 0.30 1.16 0.50 0.80
0.02 2.42 0.12 1.67 0.32 1.12 0.60 0.64
0.03 2.27 0.14 1.59 0.34 1.08 0.70 0.50
0.04 2.15 0.16 1.52 0.36 1.04 0.80 0.35
0.05 2.06 0.18 1.46 0.38 1.00 0.90 0.20
0.06 1.99 0.20 1.40 0.40 0.97 1 0
0.07 1.92 0.22 1.35 0.42 0.93 - -
0.08 1.86 0.24 1.30 0.44 0.90 - -
0.09 1.80 0.26 1.25 0.46 0.86 - -
0.10 1.76 0.28 1.20 0.48 0.83 - -